The goal of these investigations is to understand the factors which control the assembly of antibodies and their reactions with hapten. The assembly process is viewed as comprising (a) folding of the indivdual chains during and/or after synthesis, which may include closure of intrachain disulfides; (b) non-covalent association of the folded chains into a tetrameric structure and (c) covalent assembly through oxidation of the reduced half-cystine residues that form the correct interchain disulfides. Our previous work has demonstrated that covalent assembly in vitro takes place within an already non-covalently assembled tetramer. The proposed research seeks to probe, in as much chemical detail as possible, the details of interaction between isolated Fv fragments, different pairs of light and heavy chains, and modified heavy chains with light chains and light chain domains. The importance of establishing conditions for stable heavy chain-light chain combinations cannot be overstressed. Within the plasma cell, in serum and in various in vitro states, the association of heavy and light chains, or even light chain fragments, assures correct disulfide bonds, enhances solubility and protects against degradation. It is proposed also to determine whether mouse hypervariable sequences (corresponding to given specificities, such as anti-DNP, anti-phosphocholine, anti-dextran, etc.) when inserted into human framework regions, generate stable H and L chain conformations, and retain binding specificities of the original mouse proteins. We plan also to study refolding rates from denatured states of separated CL, VL and intact light chain, utilizing stopped-flow CD and stopped-flow fluorescence. Finally, in view of recent advances in understanding the structure of immunoglobulins genes, we wish to examine peptide fragments coded for by the VL and JL exons, to see whether the variable region of light chains contains an indepedently folded subdomain. The work is important not only for an understanding of the molecular basis of immunoglobulin self-assembly but has significant biomedical potential. In view of the recent mouse hybridoma techniques, the ability to incorporate specificities against tumor specific antigens and against toxins into stable human antibodies would represent a significant biomedical advance.